The [phenomenon of pee shivers] is an example of the human body's autonomic nervous system (ANS) at work.

We are not conscious of the ANS. It runs on automatic, hence its name, "autonomic", which literally means "self controlling, working independently". The urination reflex is relayed through the ANS. The reflex is directly related in strength to the amount of stretch of the bladder. Thus, the degree of shivering is generally related to how full the bladder is at the time of urination.

its funny cuz it has happened to me my whole life, no matter it i have to pee alittle or if i held it for while, i always had the shivers after i peed, it is alil orgasmic but never made me O after a piss, im glad im not alon on this

From the article: ...[T]here is a slight blood pressure rise and a momentary flushing or euphoria shortly after relaxing the urethral sphincter. Some find this feeling pleasurable. Indeed. From personal experience, I can tell you that this effect (post-micturation convulsion) can be exacerbated under certain physiological conditions.

After taking a medication for several months that caused polyuria (excessive urination) as a side effect, I found that going pee-pee had all of a sudden become a nearly orgasmic experience!

Of course, the polyuria itself was pretty annoying, so an adjustment in dosage put an end to all the, um, fun.